Method and facility for producing silane

ABSTRACT

Silane is produced in a continuous process by disproportionating trichlorsilane in at least 2 recreation areas for reaction/distillation, which are run through by a countercurrent of steam and liquid in the presence of catalytically active solid under a pressure which ranges between 500 mbar and 50 bar.

[0001] The present invention refers to a continuous process forproducing silane SiH₄ by catalytically disproportionatingtrichlorosilane SiHCl₃ to SiH₄ and silicon tetrachloride SiCl₄. Theinvention also refers to a facility for carrying out the aforesaidprocess.

[0002] SiH₄ is an excellently suitable starting material which,following further purification if necessary, can be pyrolysed in orderto separate very pure, semiconductor-quality silicon. The demand forhigh-purity silicon is growing strongly and so does the demand for puresilane whose excellent suitability for the production of high-puritysilicon is increasingly recognized and utilized.

[0003] Among the processes for producing silane described in theliterature, the production from trichlorosilane by means ofdisproportionation is advantageous from an economic point of view. It isknown that amines, in particular tertiary amines and theirhydrochlorides and quaternary ammonium chlorides, both in liquid form(DE 3 500 318 A1) and in solid form, e.g. bound to solid carriers, canbe used as catalysts in order that the disproportionation oftrichlorosilane be accelerated in an economically advantageous manner.Amines bound to solid carriers (U.S. Pat. No. 4,701,430, U.S. Pat. No.5,026,533, DE 3 500 318 A1, DE 3 311 650 C2, DE-OS-2 507 864) arepreferably used since in this way impure amines can be prevented frombeing dragged into the reacting gaseous/liquid silane/chlorosilanephase.

[0004] Liquid catalysts, as selected in some of the processes described,are disadvantageous in that they are gradually dragged out of thereactor since they can in no case be separated completely from thereaction products. The amounts of catalyst dragged along cause problemsin subsequent process steps, or also in upstream process steps in caseof a circulation system, since they can collect at certain places of thesystem and e.g. catalyse undesired reactions there. In addition, aliquid catalyst cannot be successfully distributed in the column asevenly as possible, but it will concentrate locally due to its specificsteam pressure. This problem is not at all solved, but at the mostreduced, by using two catalysts having different boiling points assuggested in DE 3 500 318 A1.

[0005] As a rule, the disproportionation of trichlorosilane is carriedout in several steps, for example in two steps. Attempts have been madefor individual steps of disproportionation to take place according tothe principles of reactive distillation. Reactive distillation ischaracterized by combining reaction and separation by means ofdistillation in one apparatus, particularly in a column. By continuallyremoving the lowest-boiling component in each element of space by meansof distillation, an optimum gradient between the state of equilibriumand the actual content of lower-boiling components or the lowest-boilingcomponent, respectively, is maintained at any time so that a maximumreaction velocity results. For example, JP 01 317 114 indicates areactive distillation process for the step of disproportionatingdichlorosilane to silane and a trichlorosilane/silicon tetrachloridemixture.

[0006] DE OS-2 162 537 also indicates a reactive distillation processfor the aforesaid disproportionation step. In addition, DE OS-2 162 537also shows a reactive distillation process for the step ofdisproportionating trichlorosilane to dichlorosilane and silicontetrachloride. DE OS-2 507 864 discloses a process for producing silanewhich is characterized in that trichlorosilane is introduced into a bedof an anion exchange resin which is not soluble in the reaction mediumand contains tertiary amino groups or quaternary ammonium groups on acarbon atom and the temperature of the resin bed is maintained such thattrichlorosilane is disproportionated into products which ascend in thebed, on the one hand, and silicon tetrachloride which condenses andflows to the bottom of the column, on the other, and in that thetemperature at the upper part of the bed is maintained above the boilingpoint of silane and below the boiling point of monochlorosilane andsilane which is virtually free from chlorosilanes is obtained from thebed.

[0007] The aforesaid process distinguishes itself from the other knownprocesses in that

[0008] (1) it is a single-stage process as regards equipment, i.e. thedesired enriched products silane and silicon tetrachloride can beremoved at different places of one and the same apparatus so thatrelatively few equipment and a reduced amount of energy are required, inthat

[0009] (2) it permits the products silane (in concentrations between 96and 98% SiH₄) and silicon tetrachloride (in concentrations e.g. between70 and 80% SiCl₄) to be produced in relatively high concentrations withno further auxiliary aggregates being needed, in that

[0010] (3) only minimum amounts of impurities are dragged from thecatalyst into the reaction mixture thanks to the solid insolublecatalyst (hereinafter referred to as catalytically active solid matter)and a considerably lower separation effort for separating off thecatalysts is required, compared to liquid soluble catalysts, and thecollection of volatile, liquid catalysts in certain sections of thecolumn is strictly avoided, and in that

[0011] (4) the amount of energy required for separating the silanes orchlorosilanes forming during the individual stages of equilibrium of thedisproportionation process is reduced due to the principle of reactiverectification.

[0012] However, a serious disadvantage of the aforesaid processdescribed in DE OS-2 507 864 consists in that the amount of energy usedfor separating the silanes or chlorosilanes has to be carried awaycompletely at a very low temperature level corresponding to thecondensation temperatures. According to DE OS-2 507 864, the temperatureat the top of the column has to be set below the condensationtemperature of monochlorosilane SiH₃Cl, while the temperature in thetrichlorosilane SiHCl₃ inlet area has to be set such that it enablestrichlorosilane to be evaporated. Thus the energy required forevaporating the various chlorosilanes and silane in the individualsections of the column is finally carried away at a temperature belowthe condensation temperature of monochlorosilane, i.e. below −50° C.down to −120° C., depending on pressure. As is generally known, carryingaway heat at low temperature levels is costly and causes additionalenergy consumption, with costs and energy required increasing the lowerthe temperature of the cooling medium has to be set.

[0013] The object of the invention is to indicate a continuous processas well as a facility for producing silane by catalyticallydisproportionating trichlorosilane to silane and silicon tetrachloride,in which process disproportionation takes place by means ofreaction/distillation on catalytically active solid matter and silaneand silicon tetrachloride are obtained in relatively high concentrationswhile the ell-ort required for separating the disproportionated productsand condensing them is reduced to a minimum. Heat is to be substantiallycarried away at a temperature level at which coolants having atemperature that can be achieved without great effort can be used inorder to reduce the equipment and energy effort required to produce coldwhich is needed to carry away heat in order to condense the products.

[0014] According to the invention, a continuous process for producingSiH₄ by catalytically disproportionating trichlorosilane SiHCl₃ tosilane SiH₄ and silicon tetrachloride SiCl₄ has been developed, whichprocess is characterized in that disproportionation is carried out in atleast 2 reaction areas for reaction/distillation containingcatalytically active solid matter under a pressure which ranges between500 mbar and 50 bar, wherein the lower-boiling product mixturecontaining SiH₄ produced in a first reaction area is intercondensed at atemperature ranging between −40° C. and 50°, the product mixture whichhas not been condensed during the aforesaid step and which is enrichedwith highly volatile chlorosilanes, particularly with dichlorosilaneSiH₂Cl₂, monochlorosilane SiH₃Cl and silane SiH₄, is passed into atleast one further reaction area for reaction/distillation and themixture which has been condensed in the intercondenser, which isenriched with low-volatility chlorosilanes and contains high amounts oftrichlorosilane SiHCl₃ and silicon tetrachloride SiCl₄ in particular, isrecycled into the first reaction area.

[0015] Advantageously, the lower-boiling product mixture containing SiH₄which has been produced is partially or completely condensed in the topcondenser.

[0016] It is preferred that disproportionation be carried out in 2 to10, particularly preferred in 2 to 5 and even more preferred in 2,reaction areas for reaction/distillation.

[0017] Suitable catalytically active solid matter is known and, forexample, described in DE-OS-2 507 864. Suitable solid matter includes,for example, solid substances in which amino groups or alkylene aminogroups are carried on a frame of polystyrol cross-linked bydivinylbenzol. Amino groups or alkylene amino groups include, forexample: dimethylamino, diethylamino, ethylmethylamino,di-n-propylamino, di-iso-propylamino, di-2-chloroethylamino,di-2-chloropropylamino groups and their hydrochlorides or thetrialkylammonium groups which are produced therefrom by means ofmethylation, ethylation, propylation, butylation, hydroxyethylation orbenzylation and contain chloride as counterion. Of course, catalyticallyactive solid matter containing other anions, e.g. hydroxide, sulphate,hydrogen sulphate, bicarbonate and others, can be introduced into theprocess according to the invention in the case of quaternary ammoniumsalts or protonated ammonium salts. However, conversion into thechloride form will inevitably occur as time passes due to the reactionconditions, even in the case of organic hydroxy groups. Thereforeammonium salts containing chloride as counterion are preferred.

[0018] Suitable catalytically active solid matter also includes, forexample, solid substances consisting of a frame of polyacrylic acid,especially a frame of polyacrylamide, which has boundtrialkylbenzylammonium, e.g. via an alkyl group.

[0019] Another group of catalytically active solid matter suitable forthe process according to the invention includes, for example, solidsubstances in which sulphonate groups are bound to a frame of polystyrolcross-linked by divinylbenzol, the cationic companions of the sulphonategroups being tertiary or quaternary ammonium groups.

[0020] As a rule, macroporous or mesoporous exchange resins are moresuitable than gel resins. Further suitable catalytically active solidmatter includes, for example, solid substances carrying organic aminogroups of the aforesaid type, e.g. such ones containing a3-siloxypropyldimethylamino group, bound to a rigid inorganic frame suchas silicic acid or zeolite (U.S. Pat. No. 4,701,430). The suitablecatalytically active solid matter is normally used in the form ofpearls.

[0021] A number of suitable catalytically active solid substances arecommercially available.

[0022] Several methods for activating and pretreating the aforesaidcatalysts are known to those skilled in the art.

[0023] In a preferred embodiment of the process according to theinvention, the product mixture containing SiH₄ is separated fromhigher-boiling chlorosilanes contained in the mixture beforecondensation of the SiH₄ end product takes place in order to increasethe concentration of SiH₄. The aforesaid separation takes place at thesame pressure or, preferably, at an increased pressure, compared tointercondensation, so that the SiH₄ concentration can be achieved at ahigher temperature level and thus a smaller amount of product has to becondensed while SiH₄ concentration is higher. Chlorosilane obtainedduring the separation process is suitably recycled into one of thereaction areas for reaction/distillation.

[0024] Several embodiments of the invention will hereinafter beexplained in more detail referring to drawings and correspondingexemplary embodiments. In the drawings:

[0025]FIG. 1 shows a facility for producing silane which comprises tworeaction areas for reaction/distillation, an intercondenser and anintegrated rectifying section and an external top condenser forcondensing silane arranged downstream of the rectifying section;

[0026]FIG. 2 shows a facility for producing silane which comprises tworeaction areas for reaction/distillation, an intercondenser, anintegrated rectifying section and an integrated top condenser forcondensing silane;

[0027]FIG. 3 shows a facility for producing silane which comprises tworeaction areas for reaction/distillation, two intercondensers and anintegrated rectifying section and an external top condenser forcondensing silane arranged downstream of the rectifying section;

[0028]FIG. 4 shows a facility for producing silane which comprises tworeaction areas for reaction/distillation, an intercondenser and anintegrated rectifying section, an external condenser arranged downstreamof the rectifying section, a separating column arranged downstream ofthe foregoing and a top condenser for condensing silane coupled to theseparating column;

[0029]FIG. 5 shows an embodiment in which the reactors are arrangedexternally.

[0030]FIG. 1 shows a process diagram of a facility for continuouslyproducing silane SiH₄ which comprises a reaction column 1 includingreaction areas for reaction/distillation 2 and 7 for catalyticallydisproportionating trichlorosilane SiHCl₃. Disproportionation in thereaction areas 2 and 7 takes place in catalyst beds each of whichconsists of a layer of bulk material which is made up of solid bodiesformed of catalytically active solid matter and through which thedisproportionation products can flow. Instead of a layer of bulkmaterial, the reaction area can also be provided with packed catalystbodies.

[0031] SiHCl₃ is supplied into the reaction column 1 via an inlet 3which opens into the column at a suitable place. For example, the inletcan open into the stripping section 4, into the area between thereaction area for reaction/distillation 2 and the stripping section 4,into the reaction area for reaction/distillation 2, into theintercondenser 6 and/or into the reaction area for reaction/distillation7. In the reaction areas 2 and 7, SiHCl₃ is disproportionated to producea vaporous product mixture which contains SiH₄ and ascends in thereaction area and a liquid mixture which contains SiCl₄ and flows out ofthe reaction area.

[0032] The liquid which contains SiCl₄ and flows out of the reactionarea is introduced into a stripping section 4 which works by means ofdistillation and is arranged below the reaction areas forreaction/distillation 2 and 7 in the reaction column 1 and below whichstripping section 4 a bottom evaporator 5 is arranged out of which thebottom product silicon tetrachloride SiCl₄ flows off via an outlet 14.The heat required for disproportionating SiHCl₃ is supplied into thereaction column via the heat exchanger 5.

[0033] An intercondenser 6 for the product mixture containing SiH₄ andascending in the reaction area 2 is provided above the reaction areas 2and 7, in which intercondenser the concentrations of SiH₄, SiH₃Cl andSiH₂Cl₂ in the product mixture are increased by partially condensinghigher-boiling components at a temperature between −40° C. and 50° C.,preferably between −5° C. and 40° C. The heat of condensation is carriedaway by a cooling medium flowing through the intercondenser 6. Thelower-boiling product components which have not been condensed in theintercondenser 6 are supplied into a second reaction area forreaction/distillation 7 which is arranged downstream of theintercondenser, in the direction of flow of the ascending productcomponents, and subsequently to a rectifying section 8 in order tofurther increase their concentration. In the exemplary embodimentaccording to FIG. 1 the rectifying section 8 is inserted above thereaction area for reaction/distillation 7 and integrated into thereaction column 1. The rectifying section can, however, also be arrangedoutside the reaction column. The product mixture exiting from therectifying section 8 is finally supplied from the top of the reactioncolumn into a top condenser 10 via an exhaust 9, condensed there and theSiH₄ end product obtained carried away in liquid state via an SiH₄product pipe 11. Part of the SiH₄ obtained is recycled to the top of thereaction column 1 via a branch pipe 12. The branch pipe 12 opens intothe column above the rectifying section 8.

[0034] The inert gaseous components produced as a rest during thecondensation of SiH₄ in the top condenser 10 are removed from the topcondenser via an inert gas pipe 13.

[0035] According to the invention in the embodiment according to FIG. 1,silane in a concentration of >70%, preferably >90%, particularlypreferred >98%, is obtained once the product removed at the top of thereaction column 1 has been condensed in the top condenser 10. Afterdisproportionating SiHCl₃ in the reaction area for reaction/distillation2 according to the invention the lower-boiling product containing SiH₄which passes from the reaction area towards the top of the reactioncolumn 1 is intercondensed. The intercondenser 6 operates attemperatures at which the heat of condensation can be carried away by acooling medium at between −40° C. and 50° C., preferably between −5° C.and 40° C., so that only a considerably smaller part of the productmixture containing SiH₄, SiH₃Cl and SiH₂Cl₂ which has not been condensedis supplied into the second reaction area for reaction/distillation 7according to the invention and to the rectifying section 8 which isequipped with the fittings normally used for distillation, such asplates and packings. Only the gas flow exiting from the rectifyingsection has finally to be condensed at very low temperatures in the topcondenser 10.

[0036] The rectifying section 8 and the associated top condenser 10 canalso be arranged outside the reaction column 1 externally.

[0037] Given the normally used pressures of between 500 mbar and 50 bar,preferably 1 to 10 bar, and the desired purities of the silane product,the top condenser 10 has to be operated below the condensationtemperatures of <−40° C., in most cases even below <−60° C. Theinstallation of separating sections which work by means of distillationonly and are arranged upstream of the condensation of the silane endproduct and the arrangement of a stripping section 4 which works bymeans of distillation above the bottom evaporator 5 enable the energyput in to be used several times, namely (1) for purifying andconcentrating silane in the rectifying section 8, (2) for continuallyremoving those products or intermediate products, respectively, whichare lower-boiling, under the prevailing local conditions as regardsequipment, by means of distillation and thus for increasing the reactionvelocity in the reaction areas for reaction/distillation 2 and 7 and (3)for purifying SiCl₄ in the lower part of the reaction column. Thestripping section 4 which works by means of distillation and thereforeenables purification of SiCl₄ removed at the bottom provides anotheradvantage, compared to the process known from DE-OS-2 507 864, since asubsequent column needed to purify SiCl₄ is no longer necessary and theamount of energy required for this process step can thus be saved.

[0038]FIG. 2 shows a second embodiment of the invention. Theconfiguration of the reaction column 1 is substantially the same as inthe embodiment according to FIG. 1. All parts of the apparatus which aredesigned analogous to the parts according to FIG. 1 are designated bythe same reference numerals. In contrast to the embodiment describedabove, the top condenser 10 in the embodiment according to FIG. 2 is notarranged externally outside the column, but integrated into the reactioncolumn 1. The integration of the top condenser 10 into the reactioncolumn 1 enables space to be saved, on the one hand, and providesadvantages with respect to industrial safety, on the other, since theholdup containing silane inside the facility is reduced.

[0039] In FIG. 3, a third embodiment is shown by way of example. Thisembodiment also substantially corresponds to the embodiment according toFIG. 1. All parts of the apparatus which are designed analogous to theparts according to FIG. 1 are designated by the same reference numerals.In the embodiment according to FIG. 3, the reaction column 1 is equippedwith two intercondensers 6 and 6′ instead of a single one. The use oftwo or more intercondensers enables the heat of intercondensation to becarried away in an exergetically advantageous manner at differenttemperature levels while the driving temperature differences are small.

[0040] Advantageously, 1 to 5 intercondensers, preferably 1 to 3,particularly preferred 1 to 2, are used according to the invention.

[0041] A fourth exemplary embodiment according to the invention isillustrated in FIG. 4. This example shows the use of a separating column15 which is arranged downstream of the reaction column 1 of theexemplary embodiment 1 and serves to further concentrate and/or purifythe product mixture containing silane. All parts of the apparatus whichare designed analogous to the parts according to FIG. 1 are designatedby the same reference numerals. In the exemplary embodiment according toFIG. 4, the separating column 15 is arranged downstream of the condenser10 which is arranged between the rectifying section 8 and the separatingcolumn 15. In the condenser 10, the non-condensed product mixturecontaining SiH₄ which exits from the rectifying section 8 via theexhaust 9 is condensed at least in part before it enters the separatingcolumn 15 so that a product mixture whose SiH₄ concentration isincreased is introduced into the separating column 15. For example, atleast 30% of the non-condensed product mixture containing SiH₄ whichexits from the rectifying section 8 via the exhaust 9 is condensed. Partof the condensate produced in the condenser 10 is recycled as a refluxliquid into the reaction column 1, above the rectifying section 8thereof, via a branch pipe 12. The remaining part of the condensate iscompressed with the aid of a liquid pump 16 and passed into theseparating column 15 via a pressure pipe 17. If only part of the productmixture exiting from the rectifying section 8 is condensed in thecondenser 10, the rest will be sucked off via an exhaust 13 by means ofa compressor 18 and supplied in a compressed form into the separatingcolumn 15 via a pressure pipe 17′. Alternatively, the flow 13 can alsobe reprocessed.

[0042] At the top of the separating column 15, there is an exhaust 19which leads to a top condenser 20 from which the produced silane whichhas been condensed and further concentrated and/or purified is carriedaway via an SiH₄ product pipe 21. Part of the liquid silane is recycledinto the separating column 15 via a branch pipe 22. Inert gaseouscomponents produced as a rest in the top condenser are carried away viaan inert gas pipe 23.

[0043] The bottom product of the separating column is carried away fromthe bottom 24 of the separating column 15 via a bottom drain 25. Part ofthe bottom product can be recycled into the reaction column 1 via thebranch pipe 26 if desired, another part is recycled into the bottom areaof the separating column 15 via a return pipe 27 once it has beenevaporated in the heat exchanger 28, yet another part can be completelyremoved from the facility (29) in order to remove impurities.

[0044] In the exemplary embodiment according to FIG. 4, a liquid orgaseous top product having lower silane purity ranging between 25% and90% is produced by reducing the amount of reflux liquid, compared to theexemplary embodiment according to FIG. 1, and by means of complete orpartial condensation in the condenser 10 in order to increase thecondensation temperature in the condenser 10 and to further reduce theenergy of condensation which has to be carried away at a very lowtemperature. In order to further purify the aforesaid top product, it isthen separated in the separating column 15 which is arranged downstreamand in which the same or, preferably, a higher pressure than in thereaction column 1, preferably between 15 bar and 100 bar, is set so thatthe separating column 15 consequently operates at higher temperaturesthan the reaction column 1, with respect to the same composition. Inthis variant, the bottom product of the separating column 15 arrangedseparately can contain amounts of trichlorosilane, dichlorosilane andmonochlorosilane, too, depending on the operating conditions which havebeen selected. The bottom product is recycled completely or in part intothe reaction column 1 via the branch pipe 26 connected to the drain 25.

[0045] The amount or amounts of feed material flowing into the reactioncolumn via the inlet pipes 3 and 26, as the case may be, are suppliedjointly or separately into the stripping section 4, into the areabetween the reaction area for reaction/distillation 2 and the strippingsection 4, into the reaction area for reaction/distillation 2, into theintercondenser 6 and/or into the reaction area for reaction/distillation7, following a preliminary reaction in a pre-reactor if necessary anddepending on the respective composition of the feed material.

[0046] The process according to the invention is carried out atpressures which range between 500 mbar and 50 bar, preferably between 1bar and 10 bar, particularly preferred between 2 bar and 5 bar, in thereaction area for reaction/distillation and using catalytically activesolid matter. The pressures serve to influence the temperatures in thesystem. In those sections of the reaction areas forreaction/distillation where disproportionation takes place, temperaturesrange between −10° C. and 180° C., preferably between 20° C. and 110° C.The temperature to be set depends on the range of stability of thecatalytically active solid matter used.

[0047] A disadvantage of the previously described processes forseparating pure silane by means of distillation concurrently with areaction process consists in the great amount of heat which has to becarried away at the condensation temperature of silane at a givenpressure, i.e. at between −50° C. and −120° C., for example.Condensation at the aforesaid temperatures is very disadvantageous froman economic point of view, as explained above. The amount of heat to becarried away if no intercondenser is used roughly equals the amount ofheat supplied at the bottom of the reaction column so that the costs forcarrying away heat will in general be considerably higher than the costsfor supplying heat. This is largely avoided thanks to theintercondensation process according to the invention. For example, asmuch as between 60% and 97% of the heat of condensation to be carriedaway can already be carried away during intercondensation, depending onthe pressure in the system, if a 25° C. warm cooling medium is used forintercondensation in order to cool down the gas flow exiting above theintercondenser and/or above the intercondensers to 40° C. so that onlybetween 3% and 40% of the heat of condensation have to be carried awayat the condensation temperature of silane. Nonetheless, silane can besuccessfully purified upstream of the intercondenser, in a separatingcolumn arranged on top of the upper reaction area 7 and/or separately,to achieve a purity of preferably more than 90% SiH₄, particularlypreferred more than 98% SiH₄, wherein the condenser which is suitablefor condensing silane and is arranged at the top of the separatingcolumn is operated using a coolant temperature being below thecondensation temperature of silane.

[0048] The facilities according to the invention preferably containfittings inside the reaction columns which guarantee an intense masstransfer between the gaseous and liquid phases and at the same timepermit an intense contact with the solid catalyst. Due to thecombination of mass transfer and reaction, a sufficient distance fromthe respective chemical reaction equilibrium is guaranteed in thereaction areas for reaction/distillation by rapidly separating productswhich are forming so that the reaction always takes place at a highreaction velocity. Examples of such fittings are plates, packings orpacking bodies for introducing heterogeneous catalysts, as they aredescribed e.g. in the following publications: EP 670 178 A2, EP 461 855A2, U.S. Pat. No. 5,026,459, U.S. Pat. No. 4,536,373, WO 94/08681 A1, WO94/08682 A1, WO 94/08679 A1, EP 470 655 A1, WO 97/26971 A1, U.S. Pat.No. 5,308,451, EP755 706 A1,EP781 829 A1, EP428265 A1, EP448884 A1, EP640 385 A1, EP 631 813 A1, WO 90/02603 A1, WO 97/24174 A1, EP 665 041A1, EP 458 472 A1, EP 476 938 A1 and in the German utility model 298 07007.3. However, the catalytically active matter, either as such or in anagglomerated form, can also be spread onto distillation plates. In theprocess, the dwell time, the volume of the catalytically active matterand the separating effect brought about by distillation in the reactionarea are adapted to the reaction kinetics and mass transfer kinetics,with the optimum as regards parameters strongly depending on the generalconditions such as e.g. the type of catalytically active matterselected, the material system and the pressure and temperatureconditions selected.

[0049] Alternatively, the catalytically active solid matter can beintroduced into external reactors, which can be temperature-controlledif necessary, while the liquid phase is alternately passed from thereaction column into the reactor and from the reactor back into thereaction column for the purpose of material separation. In order todecouple different temperatures within the reaction column and inexternal reactors, the material flows between the reaction column andthe reactors can be temperature-controlled.

[0050]FIG. 5 shows an embodiment according to the invention in which thereaction areas for reaction/distillation 2 and 7 of FIGS. 1 to 4 havebeen replaced with externally arranged reactors. The liquid mixtureflowing out of a distillation section 30 enters a reactor 33, via heatrecovery 31 and temperature control 32 if necessary, in which reactorthere is a flow from top to bottom or from bottom to top, from which itpasses into the next distillation section. The “distillationsection/temperature control/reactor” sequence can be arranged one abovethe other as many times as desired.

[0051] According to the invention, the disproportionation process takingplace in the reaction areas of the reaction columns is supplemented byseparation and purification of the products containing silane and/orsilicon tetrachloride which are to be removed at the top and bottom ofthe reaction columns, which separation/purification is brought about bydistillation only. The separation by means of distillation is carriedout with the aid of fittings which are usually employed for puredistillation, such as plates, packings and packing bodies. As regardsthe higher-boiling SiCl₄ component flowing out, it is advantageous, bymeans of separation using pure distillation taking place below thereaction area for reaction/distillation in the lower part of thereaction column to produce highly concentrated silicon tetrachloridecontaining more than 70% SiCl₄, preferably more than 95% SiCl₄,particularly preferred more than 99% SiCl₄, as a bottom product which isremoved from the bottom of the reaction column. List of referencenumerals Reaction column  1 Reaction area for reaction/distillation  2SiHCl₃ inlet  3 Stripping section which works by means of distillation 4 Bottom evaporator  5 Intercondenser 6, 6′ Reaction area forreaction/distillation  7 Separating section which works by means ofdistillation  8 Vapour exhaust  9 Top condenser 10 SiH₄ product pipe 11Branch pipe 12 Vapour exhaust pipe 13 SiCl₄ outlet 14 Separating column15 Liquid pump 16 Pressure pipe 17 Compressor 18 Vapour exhaust 19 Topcondenser 20 SiH₄ product pipe 21 Branch pipe 22 Vapour exhaust pipe 23Bottom 24 Bottom drain 25 Branch pipe 26 Return pipe 27 Evaporator 28Removal 29 Distillation section 30 Heat recovery 31 Temperaturecontrol/heat exchanger 32 Reactor 33

1. A continuous process for producing silane SiH₄ by catalyticallydisproportionating trichlorosilane SiHCl₃ to silane SiH₄ and silicontetrachloride SiCl₄ characterized in that disproportionation is carriedout in at least 2 reaction areas for reaction/distillation containingcatalytically active solid under a pressure which ranges between 500mbar and 50 bar, wherein the lower-boiling product mixture containingSiH₄ produced in a first reaction area for reaction/distillation isintercondensed at a temperature ranging between −40° C. and 50° C. andthe product mixture which has not been condensed during the aforesaidstep and which is enriched with highly volatile chlorosilanes,particularly with dichlorosilane SiH₂Cl₂, monochlorosilane SiH₃Cl andsilane SiH₄, is passed into at least one further reaction area forreaction/distillation and the mixture which has been condensed in theintercondenser, which mixture is enriched with low-volatilitychlorosilanes and contains in particular high amounts of trichlorosilaneSiHCl₃ and silicon tetrachloride SiCl₄, is recycled into the firstreaction area.
 2. A process according to claim 1 characterized in thatthe lower-boiling product mixture containing SiH₄ produced is partiallyor completely condensed in the top condenser.
 3. A process according toat least one of claims 1 or 2 characterized in that, in total, severalintercondensations at different temperature levels ranging between −40°C. and 50° C. are carried out between the reaction areas.
 4. A processaccording to at least one of claims 1 through 3 characterized in thatthe pressure in the reaction areas is between 1 and 10 bar.
 5. A processaccording to at least one of claims 1 through 4 characterized in thatthe intercondensations take place at temperatures ranging between −10°C. and 50° C.
 6. A process according to at least one of claims 1 through5 characterized in that the product mixture produced in the topcondenser is subjected to a subsequent reprocessing during which it isseparated at an increased pressure, compared to disproportionation.
 7. Aprocess according to claim 6 characterized in that chlorosilanesobtained during the reprocessing of the product mixture produced in thetop condenser are recycled, at least in part, into the reaction area forreaction/distillation.
 8. A process according to at least one of claims1 through 7 characterized in that the silane content of thelower-boiling product produced in the reaction areas is increased to aconcentration of >50% by weight by means of distillation in a separatingsection and the product mixture whose concentration has thus beenincreased is supplied into the top condenser.
 9. A facility forproducing silane SiH₄ in a continuous manner by disproportionatingtrichlorosilane SiHCl₃ to silane SiH₄ and silicon tetrachloride SiCl₄ ina reaction column comprising an SiHCl₃ inlet and a top condenser, whichis either connected to the reaction column or integrated into therejection column, for condensing product containing SiH₄ produced and anexhaust for condensed SiH₄ arranged at the top condenser and an outletarranged at the reaction column for SiCl₄ produced as a bottom product,which facility is characterized in that the reaction column comprises atleast 2 reaction areas for reaction/distillation arranged one above theother and comprising catalyst beds which contain solid bodies formed ofcatalytically active solid matter and through which thedisproportionation products and trichlorosilane can flow and in that atleast one intercondenser is arranged between the lower one of thereaction areas for reaction/distillation and the top condenser, whichintercondenser is operated at a temperature ranging between −40° C. and50° C.
 10. A facility according to claim 9 characterized in that anintercondenser is arranged between 2 reaction areas forreaction/distillation which are located one above the other.
 11. Afacility according to at least one of claims 9 through 10 characterizedin that a temperature ranging between −5° C. and 40° C. is set in theintercondenser.
 12. A facility according to at least one of claims 9through 11 characterized in that several intercondensers are arrangedbetween the lowest one of the reaction areas for reaction/distillationand the top condenser.
 13. A facility according to claim 12characterized in that the intercondensers are arranged above reactionareas for reaction/distillation each.
 14. A facility according to atleast one of claims 9 through 13 characterized in that downstream of theuppermost intercondenser, in the direction of flow of the lower-boilingproduct mixture flowing off the intercondenser a reaction area forreaction/distillation and a rectifying section are arranged, in whichthe concentration of silane SiH₄ in the product mixture is increased bymeans of distillation.
 15. A facility according to at least one ofclaims 9 through 14 characterized in that downstream of the uppermostintercondenser, in the direction of flow of the lower-boiling productmixture flowing off the intercondenser, a separating column is arrangedfor separating product components containing SiH₄ from higher-boilingchlorosilane components.
 16. A facility according to claim 15characterized in that the separating column is arranged downstream of arectifying section according to claim
 14. 17. A facility according toclaim 16 characterized in that a condenser is arranged between therectifying section and the separating column.
 18. A facility accordingto at least one of claims 15 through 17 characterized in that theseparating column operates at an increased pressure, compared to theintercondenser, and the product passed into the separating column iscompressed.
 19. A facility according to at least one of claims 15through 18 characterized in that a branch pipe is connected to thebottom drain of the separating column, which branch pipe opens into areaction area for reaction/distillation of the reaction column.